Method and apparatus for effecting channel acquisition

ABSTRACT

Methods of and corresponding apparatus for scheduling messages on an operating channel (223) in a selective messaging system (200) for a messaging unit (235) include scheduling a first message, including a channel priority indication (511), addressed to the selective messaging unit on a first channel, and then scheduling a second message for the selective messaging unit on a second channel (225) selected as an alternative operating channel. Analogously at the selective messaging unit a method of selecting an operating channel includes monitoring the first channel for a message addressed to the selective messaging unit; detecting as part of the message the indication; and responsive thereto discontinuing monitoring the first channel and then scan for the second channel.

FIELD OF THE INVENTION

This invention relates generally to communication systems and morespecifically but not limited to methods and corresponding apparatus foreffecting channel acquisition.

BACKGROUND OF THE INVENTION

Communications systems, especially messaging and paging systems,typically operate on a channel having a specified radio frequency for asubscriber's home location. These systems are viable solutions as longas the channel and radio frequency have the spectral capacity toaccommodate or provide service to all subscribers or users of thesystem. As the number of subscribers and the mobility of thosesubscribers increase, these systems may begin to experiencedifficulties. Adding capacity may require additional channels and radiofrequencies. Assuming the demands for capacity can be met at one oranother location, subscribers traveling between locations typically findthat the two locations do not share a common radio frequency or channel.These subscribers may be required to carry and maintain a messaging unitor pager for each of the locations the subscriber might be traveling to,or one pager that can be adjusted to each local channel. This is aconstraint and significant inconvenience for subscribers that needmessaging or paging coverage in multiple locations.

As subscribers demanded messaging and paging service in multiple areas,practitioners sought solutions that provided the subscriber the abilityto move between paging areas and have the convenience of carrying asingle subscriber unit. This demand and these concerns spawned theconcept of roaming in the paging industry or for paging systems. Roamingrelates to the ability of a subscriber to have service in a paging areaknown as a home area, and additionally have the option of temporarilyextending this service outside of the home area.

Messages for the subscriber are ordinarily sent by the home system onthe home system channel and radio frequency to the subscriber. When asubscriber knows they will be traveling out of the home area, theycontact the service provider via telephone to advise the provider as towhen and where the subscriber expects to travel. With this informationthe service provider forwards messages for the subscriber to those areasbeing visited during the times agreed upon. Capacity on the home systemand other areas is not wasted as the message need not be broadcast inthe home area or other areas when the service provider knows thesubscriber is not present.

Messaging units operating on multiple frequencies have been built. Thesemultiple frequencies represent valid frequencies in various pagingsystems and allow the messaging unit to operate in or roam to systemswith different frequencies; however the messaging unit needs to betuned, typically manually, to the proper channel. The concept of roamingrelies on the cooperation and coordination of both the service provideror system and the subscriber or unit to ensure the continuity of serviceover multiple service areas for specified periods of time. Prior art hasprovided for roaming that included coverage within the home area androaming areas by ensuring that messages are sent to all the differentcoverage areas the subscriber might be located in at least during theapparent roaming times, but this may waste system capacity.

Potential issues arise when the subscriber can receive channels frommore than one system, such as the home system and either one or moreroaming or other systems at the same time. The system inefficiently usesairtime by sending duplicate messages to multiple controllers orsystems, or alternatively messages may be missed if the messaging unitis tuned to a channel other than the channel the system is using. Also,if the messaging unit has scanning capability, the unit can wastevaluable battery resources scanning multiple systems attempting todetermine the most appropriate channel to tune to.

Roaming systems suitable to mitigate some of these issues have beenproposed by Gaskill, et al. U.S. Pat. No. 4,897,835. Gaskill et al.suggests that the messaging system tells the messaging unit to tune to aparticular channel. Subsequent messages are broadcast only on thatchannel frequency. Drawbacks to Gaskill include sending the tuningmessage on all channels the messaging unit may be on, thus wastingcapacity, and the possibility that the messaging unit does not receivethe tuning message thus missing subsequent messages.

Clearly a need exists to automatically allow a system and a messagingunit to adequately and routinely modify and effect the operatingchannels available to subscribers.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention that are believed to be novel areset forth with particularity in the appended claims. However, theinvention together with further advantages thereof, may best beunderstood by reference to the accompanying drawings wherein:

FIG. 1 is an illustrative coverage map for a plurality of messagingsystems.

FIG. 2 is a block diagram of a selective messaging system suitable foremploying an embodiment of the instant invention.

FIG. 3 is a more detailed block diagram of a selective messaging unitsuitable for use in the FIG. 2 messaging system and in accordance withthe instant invention.

FIG. 4 is a illustrative map of contents of a memory suitable for use inthe FIG. 3 selective messaging unit.

FIG. 5 is a exemplary protocol diagram.

FIG. 6 is a flow chart of a preferred method embodiment in accordancewith the present invention.

FIG. 7 is a flow chart of an alternative preferred method embodiment inaccordance with the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The present disclosure concerns communications systems, such asselective messaging systems arranged to provide relatively wide areacoverage using multiple frequencies and more specifically methods andapparatus for use in such systems. In a preferred embodiment, set in aselective messaging unit, a method of selecting an operating channelincludes monitoring a first channel for a message intended for oraddressed to and preferably addressed only to the selective messagingunit; detecting as part of the message an indication during the step ofmonitoring; discontinuing, responsive to that indication, themonitoring; and then scanning or searching for a second channel to useas the operating channel.

Preferably the method includes providing a list of potential operatingchannels that includes the first and second channel. In one form theindication is a priority command, such as a preference or priority indexcorresponding to various channels. The list of channels is modified inaccordance with this priority command to provide a modified list, andthen the step of scanning for channels within the modified list toprovide the second channel is preferred. In many instances the best ormost likely channel to use as an operating channel or a second channelwill be a channel, such as one corresponding to or providing coverage ata diverted or destination location, a previous location, or anintermediate location. The step of discontinuing or the start of thescanning step may be undertaken at a time corresponding to informationwithin the indication. Alternatively the indication may be interpretedas an affirmation signal to remain on the current channel and thescanning step thus foregone.

An alternative embodiment is set in a selective messaging system and isa method of scheduling messages on an operating channel for a selectivemessaging unit. The method includes first scheduling a first message foror addressed to the selective messaging unit on a first channel, thefirst message including a channel priority indication corresponding tothis first channel thus causing the unit to scan; and second schedulinga second message for the selective messaging unit on a second channel,the second channel selected as the operating channel from a plurality ofchannels as an alternative to the first channel. This second channelwill also be selected by the unit during its scan.

Preferably the step of second scheduling includes scheduling the secondmessage on each channel or other subset of the plurality of channels.The plurality of channels is included as a part of a list of potentialoperating channels for the unit provided for example to the system by asystem operator at the time of service initialization. The step of firstscheduling preferably further includes formulating the channel priorityindication to correspond to a relative priority of channels within theplurality of channels. In certain conditions it will be advantageous toschedule the second message on a channel for a diverted location, or aprevious location, or an intermediate location. The second schedulingstep is preferably conducted or undertaken at a time determined tocorrespond to or derived from the channel priority indication.

A corresponding apparatus embodiment of the present invention is aselective messaging unit arranged and constructed for selecting anoperating channel. This selective messaging unit includes a receiver formonitoring a first channel for a message intended for the selectivemessaging unit and a controller, coupled to the receiver, for detectingas part of the message an indication and responsive thereto causing thereceiver to discontinue monitoring the first channel and then scan for asecond channel to use as the operating channel. Preferably, theselective messaging unit also includes a memory for storing a list ofpotential operating channels, the list including the first channel andthe second channel. The indication, preferably, includes a prioritycommand that will be used to modify the list accordingly thus providinga modified list. The controller then cooperatively with the receiverscans channels corresponding to the modified list to provide the secondchannel. Channels included in the list or modified list mayadvantageously include a channel for or corresponding to a diverted,roaming or remote location, or a previous or local location, or anintermediate or transition location. The scanning for a new oralternative operating channel or more particularly discontinuingmonitoring the first channel is, preferably, done or undertaken at atime determined to correspond to the indication. Alternatively theindication may be interpreted as an affirmation of the first channel asan operating channel in which case the scanning step would be foregone.

A further embodiment is a messaging system controller adapted forscheduling messages on an operating channel for a selective messagingunit. The messaging system controller includes a processor forscheduling a first message for the selective messaging unit on a firstchannel, the first message including a channel priority indication orpriority indication or simply indication corresponding to the firstchannel; thereafter the processor schedules a second message for theselective messaging unit on a second channel, the second channelselected as the operating channel from a plurality of channels as analternative to the first channel; and a transmitter port for couplingthe first message and the second message to respective or correspondingtransmitters. The second message is preferably scheduled by theprocessor on each channel of the plurality of channels at least for someperiod of time after which the processor may schedule the second messageor messages thereafter on only one channel of the plurality of channels.

The system controller preferably includes a memory or database forstoring a list of potential operating channels for the selectivemessaging unit as well as all other messaging units in the system, wherethese lists include the plurality of channels corresponding to eachmessaging unit. The processor while first scheduling, preferably,further formulates the channel priority indication to correspond to arelative priority of channels within the plurality of channels. Theprocessor may advantageously schedule the second message on a channelfor a diverted or remote location, or a previous or local location, oran intermediate or transition location and at a time determined tocorrespond to the channel priority indication.

For a clearer understanding of the present disclosure the reader isreferred to the FIG. 1 representative messaging system coverage map. Aregion wide area or location (100) serviced by a region wide channel orfrequency represents and provides system coverage for a selectivemessaging unit in or throughout a region wide geographic area. Theregional system controller (101) operates to schedule messages for theselective messaging units within the region. The home area or location(103) and thus home channel or frequency represents and provides by wayof a home terminal (104) and a system controller (106) operatingtogether, messaging system coverage for a subscriber or pager orselective messaging unit in a home or local or normal geographiclocation. This home area may be a previous location for the selectivemessaging unit if the unit is transported or otherwise redirected toanother system's coverage area. When the subscriber or pager orselective messaging unit desires to obtain messaging coverage outside ofthe home location, a form of roaming capability allows for coverage in aremote, roaming, or diverted location (107) via a diverted or roamingfrequency and channel. The diverted system controller (112)cooperatively works with the home terminal (104) via leased telephonelines, radio, or satellite links to facilitate the roaming operation.The intermediate system controller (110) works with the home terminal(104) as the subscriber or pager or selective messaging unit travelsbetween the home area, and the diverted or roaming or remote location(107), to provide coverage in the intermediate location (105) on acorresponding frequency and operating channel.

Various concerns or issues, arising as a result of these overlappingcoverage areas, many that are or may be addressed by the inventiveprinciples developed herein will be more apparent if we consider thecircumstances faced by a selective messaging unit as it traverses path(115) beginning at the home point (116). At point (116) coverage ispreferably provided by the home system thus reserving capacity in othersystems such as the region wide system (100) for traffic or messagesthat must use those systems. As our selective messaging unit moves orroams to point (117) home system coverage is lost and the regionalsystem with coverage area (101) must or should handle any messages forthe selective messaging unit. Continuing at point (118), messages forour selective messaging unit are preferably handled by the diverted orremote system and at point (119) by the intermediate system (110). Thebalance of these discussions will be directed to various inventiveprinciples and operations for fulfilling or insuring that selectivemessaging units have appropriately selected operating channels such thatmessages for the unit may be delivered on the appropriate system thusavoiding undue capacity inefficiencies.

Continuing the present disclosure the reader is referred to the FIG. 2depiction of a representative paging or messaging system (200),preferably, a selective one-way messaging system, but alternatively atwo-way messaging system, communicating with a plurality of messagingunits (235, 237). The messaging system (200) includes a gateway orterminal (203), exemplified by the home terminal (104), coupled to amessage source such as the public switched telephone network (201). Theterminal (203) is available from Motorola as the WMG™ product as well asfrom other manufacturers. The terminal is coupled to, often collocatedwith, a system controller or controller (205), such as a Motorola RFCONDUCTOR™ suitably modified with the inventive principles discussedherein. The terminal (203) and system controller (205), coupled togetherby switch port (202) operate together to communicate messages withdestination addresses for various messaging units (235, 237) from theterminal (203) to the system controller (205) or various responses, inthe case of a two-way system, back to the terminal (203), thus to thePSTN (201) and the originator. The region wide system controller (101),the home system controller (106), the intermediate system controller(110), and the diverted system controller (112) are examples of thesystem controller (205).

The messaging system (200) includes, coupled to the controller (205),via a transmitter port (206), by the outbound network channel (207), aplurality of transmitters with five depicted as a first through 5thtransmitter (211 . . . 215). The transmitters are available, forexample, as Motorola NUCLEUS II™ transmitters or from other suppliers.The outbound network channel (207) is preferably leased telephone linesbut may be any suitable media operating with any suitable networking orcommunication protocol including a radio or satellite link. The system,specifically controller and transmitters are arranged and constructedand operate to provide coverage and service in one or more geographicareas or service areas such as the region wide area or home areamentioned above. It is understood that the FIG. 2 system is exemplaryonly and that much other equipment not here shown nor here relevant maybe required in a practical system.

Additionally, the messaging system (200), when a two-way system,includes, coupled to the system controller (205), via a receiver port(210), by a network channel (209), a plurality of base receivers, suchas four depicted base receivers (217-220). The network channel ispreferably leased telephone lines or any other suitable network linkwith the bandwidth necessary for the traffic expected on the channel.Typically at least some of the base receivers will be deployed atgeographic locations different from the transmitters and typically morereceivers are deployed than transmitters.

Generally the messaging system is a scheduled system using a protocolsuch as the FLEX™ one-way or ReFLEX™ two-way protocols by Motorola whereall messages outbound or inbound are transmitted within time slots in atime frame on an outbound or inbound channel (223, 229) each normally adifferent radio frequency. Typically within a given system alltransmitters operate on the same outbound frequency or channel and oftenin a simulcast (nearly identical launchtime) mode. In contrast systemsproviding overlapping coverage such as the home and region wide systemswill normally operate on a different channel. The system controllerprovides control of the system including scheduling outbound or inboundmessages for messaging units that are registered on or subscribe to thesystem's services. The system controller (205) is responsible formaintaining the schedule, designating what channel(s) if need be andrespective transmitter(s) or radio frequency(ies) and when within theoverall schedule for each channel, a message for a messaging unit willbe transmitted, notifying messaging units of the time slot where theywill receive messages and, if two way units, during what inbound timeslot they are expected to acknowledge receipt of the message and whatinbound slots are available for volitionally originated messages,according to a slotted ALOHA contention algorithm.

The outbound messages are forwarded to the transmitters for subsequenttransmission to one or more messaging units, such as the depictedmessaging units (MU) (235, 237) in accordance with the system protocolat a particular time on the forward or outbound radio channels (225).Messages originating at the messaging unit (235), either volitionally asin a registration request or responsive to a received message, such asan acknowledgment, are coupled by the reverse or inbound radio channel(229) to one or more of the base receivers where they are forwarded orrelayed to the system controller on the inbound or network channel(209). The system controller may use these inbound messages forscheduling decisions, such as repeats, may forward them to the terminal,if, for example, they are intended for a user destination, or may usethem to perform various traffic analysis and system management orconfiguration functions.

Referring to the more detailed diagram of the system controller (205),the operation and basic structure of the controller will be explained.As above noted the controller or messaging system controller is adaptedfor scheduling messages on a channel or an operating channel. Themessages are intended for or addressed to and scheduled for a specificselective messaging unit. The messaging system controller includes aprocessor (231) that is, preferably based on a 32 bit SuperSPARCmicroprocessor designed and distributed primarily by SunMicroelectronics.

The processor (231) is coupled to the various input output ports,specifically switch, transmitter, and receiver ports (202, 206, 210) andfurther coupled to a memory (233). The memory is a combination of diskbased and RAM based storage suitable for storing all operating softwareas well as database information required by the system controller (205).In the exemplary diagram of FIG. 2 the controller is shown as a singleentity. However it is understood that the controller and the terminal(203), either or both, may be composed of distributed terminal ordistributed controller functions or resources and may be eithercollocated or located at a plurality of physical locations. Thissituation would likely be encountered in a large paging system such asthe systems of FIG. 1. that included some form of roaming capability.Similarly while the FIG. 1 depiction shows various controllers or systemcomponents all of these functions may be resident at one location andmay be handled by one controller or gateway or switch depending onsystem loading and complexity. For the remainder of our discussion it isassumed that FIG. 2 depicts two systems having two different coverageareas. One system will be referred to as the home system and includestransmitters one and two (211, 212) and operating channel (223), and thesecond system including transmitters three, four, and five (213, 214,215) and operating channel (225) will be referred to as another,diverted, remote, region wide, etc. system as the circumstances andexplanations require.

In these roaming systems a major task for the controller is coordinationof where and when the message is scheduled with the actual location andclock of the intended messaging unit. For example if messaging unit(235) travels from a location near its home system and transmitter 1(211) to a remote location near to or within the coverage area ofanother system, such as transmitter 3 (213), some methodology is neededto properly deliver messages without wasting system capacity. Thesesystems operate on different frequencies such as channels (223, 225) anddo not have overlapping coverage at the remote location. The systemcontroller and the unit must somehow recognize that messages must bedelivered by the other system on the respective operating frequency ofthat system. Minimizing undue waste of system capacity mandates that themessage not be transmitted on all systems, rather efficient utilizationof system capacity requires that the message be transmitted only to thelocation where the messaging unit is likely to be and the system havingthe smallest coverage area that includes that location should be used.

The system controller (205) accomplishes this task, after having beeninformed usually by way of a telephone call that a user has certainlocation expectations, such as a flight to a given locale at a certaintime. More specifically the processor (231) schedules a first messageaddressed to or for the selective messaging unit on a first channel,such as channel (223), where the first message includes an indication,preferably, a channel priority indication that corresponds to the firstchannel. In the preferred form this indication is an affirmativeindication or order to the addressed selective messaging unit to leaveor discontinue monitoring the first channel and to scan through a listof channels in search of a second channel. The underlying premise beingthat if the unit looks for a better channel or alternative channel, sucha channel will be found. For example, the system controller (205) mayschedule the first message for the selective messaging unit to be sentby transmitter 1 (211) on the first or outbound channel (223).Thereafter the processor (231) schedules a second message and subsequentnormal paging messages on at least another channel, for exampletransmitter 3 (213). In fact system operators may determine that greatercustomer satisfaction results if the subsequent normal paging messagesare sent on multiple systems or a plurality of channels, such as thehome system and remote system at least for a small time periodsurrounding the expected time the user will arrive in the other system.For example, when reasonable travel delays occur, the user may stillexpect to receive messages original plans notwithstanding.

The transmitter port (206) of the system controller (205) provides forcoupling the first message and the second message and all other messagesto the corresponding transmitters. The second message for this exampleis transmitted on at least one radio frequency that is different, thuscorresponding to another system, from the frequency the first message,corresponding for example to the home system, was sent or transmittedon. The channel priority indication of the first message induces themessaging unit to scan for a second channel from the plurality ofchannels. The messaging unit (235) will continue to monitor and thusreceive messages on the second channel so long as the channel isavailable or until a message with the indication is received.

The memory (233) of the system controller (205) is used to retaininformation on a list of all the channels used by the plurality oftransmitters that are managed by the system controller (205). The listof potential operating channels for a selective messaging unit is asubset of the list of channels used by the system controller (205) andis usually determined at the time the selective messaging unit isactivated or when service is originally subscribed to. The reader isreferred to the FIG. 4 depiction of an illustrative map of contents ofmemory (401). This map generally applies to either the memory (233) ofthe system controller or the memory (321) of a selective messaging unit.In either case the memory contains the list of potential operatingchannels (Channel A thru Channel N) (403-410) for the unit. In additionto the list of channels the memory may include the operating system(412), other databases (414), and other functions (416). The memory,preferably also contains, associated with channels (Channel A thruChannel N), their corresponding priority (Priority 1 thru Priority M+2).Upon activation the selective messaging unit is provided with anoperating channel, for example channel (223) that usually has a higherpriority than other channels in the list. This higher priority channelis the outbound frequency or channel for the home location (103) and mayoccupy the channel A (403) on "top" location in memory. Other operatingchannels would have different and usually lower levels of channelpriority based on the implementation scheme of the present disclosure.

When the home system controller (103) sends messages to the selectivemessaging unit that effect channel acquisition, the message includesinformation depicted in the exemplary protocol diagram (501) shown inFIG. 5. The synchronization or sync (503) provides for synchronizing theincoming signal and the selective messaging unit and is well known. Thedata (503) portion of the message typically includes informationintended to be conveyed to the user of the selective messaging unit. TheBlock Information Words or BIW (505) is used by the system controller(205) to inform the selective messaging unit of various systemconfiguration parameters. Included in the BIW is a zone (506) thatrepresents, for example, the home, remote, roaming, or diverted locationof the selective messaging unit. The next field in the message is anaddress field (AF) and a vector field (VF) (507). This field will havean address that corresponds to a selective messaging unit and acorresponding vector that points to a location in the data or messagefield (509). At this location in the data field the indication (511) orpriority indication will, preferably, be found. This indication may takevarious forms as explained below. In the preferred form this indicationis an affirmative order to the selective messaging unit to go scan for asecond channel. In alternative forms the indication may includeinformation that alters the priority of the channels in the memory ofthe selective messaging unit. The indication or channel priorityindication may also provide temporal information, such as leave thechannel at a particular time of day or frame number. The indicationincluding timing can include various combinations such as leave channelbefore or after certain times. Additionally the indication may simplyorder the selective messaging unit to remain on the channel.

As an example of how some of these indications may be used by a systemoperator consider the circumstances where the messaging unit (235)travels from a location proximate transmitter 1 (211) to a locationproximate transmitter 3 (213). Assuming these transmitters operate ondifferent frequencies but have overlapping coverage areas such as thehome area (103) and the intermediate area (105), the system controllerand the messaging unit must somehow agree how or on what system usingwhat transmitter messages will be delivered. The processor (231)accomplishes this task, after having been informed that a user hascertain location expectations, such as a flight to a given locale at acertain time, by scheduling a first message for the selective messagingunit (235) on a first channel, such as channel (223) from transmitter 1(211), where the first message includes a channel priority indicationcorresponding to the first channel. The channel priority indication mayalso be used to informs the messaging unit (235) that the first channelis valid for a predetermined period of time after the first message issent. Upon lapse of this period of time the unit will scan for a secondchannel. The channel priority indication also adjusts, includingselectively eliminating some channels and thus leaving a plurality ofchannels, the channel priority indication or priority of the list ofpotential operating channels that the messaging unit has at itsdisposal. In this case the priority indication corresponding totransmitter 3 (213) or specifically channel (225) is increased to apriority higher than channel (223). When the unit scans it will find ordetect channel (225) and use that channel as the operating channel forfurther monitoring.

As a further example consider again a messaging unit traveling thehypothetical path (115) and how a system controller, using the inventiveprinciples such as the indication or priority indication disclosedherein, would schedule messages and thus discriminate between locations(100, 103, 105, 107). Prior to departure from the home area, point(116), the messaging unit would continuously receive messages on thehome system (103) and its corresponding first channel, such as channel(223). At the appropriate time derived from the users plans, thecontroller in location (103) will schedule and send a first messageincluding a corresponding priority indication on the outbound radiochannel (223) to the selective messaging unit. This priority indicationwill tell the selective messaging unit that the home channel is nolonger valid, possibly at a certain time and can increase the priorityof the region wide system. At the time the unit would scan and selectthe region wide channel and the controller would schedule messages onthat channel. This corresponds to the point (117) on path (115). As theselective messaging unit proceeds or more specifically as time passesand the system controller expects the unit to be at the diverted orremote location or coverage area (107), the processor (231) of thesystem controller (205) will schedule a message including acorresponding priority indication on the region wide channel. Theindication can dictate that the selective messaging unit will scan forthe second channel from a definitive start time until a specific stoptime. Again responsive to the priority indication, the unit discontinuesmonitoring the region wide channel and scans for an intermediateoperating channel. When the unit is within range of the divertedcoverage area (107), the scanning operation would select thecorresponding channel for the operating channel. The channel priorityindication can also dictate that the region wide channel will be validuntil a particular time. In any event, since the system operator cannotbe certain when the selective messaging unit, if it is a one way unit,arrives at or within the diverted coverage area (107) it may bedesirable to continue to provide messages on the previous or region widesystem even after messages are being sent on the diverted system, atleast for a short time period. Additionally a message with the priorityindication may need to be repeated on the previous or home system.Continuing with path (115) when the selective messaging unit is expectedto leave the diverted location (107) again as indicated by a phone callto the home system and travels to the intermediate location, point(119), a message is scheduled and transmitted on the diverted or remotesystem that includes an indication directing the unit to scan itschannel list.

The indication or channel priority indication in this message candictate that the diverted channel will be valid in the diverted location(107 of FIG. 1) until a particular time. The indication may alsoindicate that the diverted channel will not be valid after a particularspan of time. When the subscriber is going to the intermediate location(105), the messaging unit will have the ability to receive messages fromboth systems (105,107) while in the overlapping coverage area (see FIG.1). To facilitate resolution of which system the selective messagingunit should monitor, and thus where messages should be scheduled, theselective messaging unit must at least temporarily erase the divertedchannel from its channel list or at the optional times indicated by theindication drastically reduce its priority and increase the priority ofthe intermediate channel until it exceeds the remote channel priorityand the region wide priority. This done, the scanning operation willdetect the intermediate system. A similar situation will be encounteredas the path is traversed from point (119) to point (116). As the readermay now appreciate by selectively using or applying the variousparameters of the indication, a system and selective messaging unit canreadily coordinate activities required for roaming thus minimizing unduewaste of system resources, as well as, avoiding the excessive batterydrain at the selective messaging unit due to unnecessary scanning suchas may be experienced, for example, in selective messaging units thatperform essentially constant (background) scanning.

As a review, it is clear from the above discussions that the messagingsystem controller or controller may elect, via the processor, toschedule messages on each channel of a plurality of channels. Thisplurality of channels is selected from the list of channels that amessaging unit is programmed typically at activation to receive. Thisscheduling occurs after the message with the indication causing the unitto scan for another operating channel has been scheduled and sent atleast for a time period during which the controller is uncertain aboutthe exact location of the unit. The memory of the messaging systemcontroller must store a list of potential operating channels for eachselective messaging unit that it serves or for which it schedulesmessages. The messaging system controller prior to scheduling themessage with the indication or priority channel indication mustformulate the channel priority indication to deal with the particularcircumstances at hand, for example, to correspond to a relative priorityof channels within the plurality of channels. The formulation mustconsider as above noted where the messaging unit was receiving serviceand where the unit next expects service. For example, whether thesubsequent messages are to be scheduled on a channel for a divertedlocation, a previous location, or intermediate location, etc. inaddition to when or what time these messages should be scheduled.

The reader is referred to the FIG. 3 block diagram of a selectivemessaging unit, such as unit (235) for the following discussion. Suchselective messaging units are available from Motorola and othersuppliers and are commonly referred to as pagers. The readily availablepagers would need to be modified in accordance with the principlesdisclosed herein and this modification would normally be a change inoperating system readily implemented by one skilled in the art in viewof the principles herein. FIG. 3 depicts a selective messaging unitarranged and constructed for selecting an operating channel. The unitincludes an antenna (239), coupled to a receiver (317) and a transmitter(323). The antenna (239) operates to absorb radio signals and couplethem to the receiver (317) or alternatively to radiate radio signalscoupled to the antenna from the transmitter. The reader will appreciatethat the transmitter is available or part of the selective messagingunit only when the unit is a two-way messaging unit. The user I/O (325)is coupled to the receiver and when present the transmitter andrepresents the medium, such as displays and pushbuttons, by which theselective messaging unit and the user communicate, in appropriateformats, messages and, in the case of a two-way messaging unit,responses. The receiver includes generally known elements such asfilters, amplifiers, mixers, frequency generation units or synthesizers,demodulators, decoders, and the like and is coupled to and under thecontrol of a controller (319). The controller programs the synthesizerthus tuning the receiver to and allowing it to operate to monitor achannel and receive various messages on that channel. Once a message isdecoded or partly decoded the receiver together with the controller cancheck the address of that message with the address of the selectivemessaging unit. If there is a match the message is intended for oraddressed to this messaging unit. The selective messaging unit ofinterest for the present disclosure has been modified from the normalpager such that the controller is arranged for detecting as part of themessage intended for the unit, an indication, such as discussed above.The controller in response to the indication causes the receiver todiscontinue monitoring the first or original operating channel and thenscan for a second channel to use as the operating channel. This is doneby reprogramming a synthesizer for one or more new channel frequenciesand looking for activity such as the sync (503) portion of messages.

Further included in the selective messaging unit, coupled to thecontroller (319), is the memory (321) used for storing a list ofpotential operating channels along with some token of there priority foruse as an operating channel. The list includes the original or firstchannel and the second channel all as previously discussed withreference to FIG. 4. The indication may further include a prioritycommand and the controller will operate to modify the list, preferablythe token designating priority, in accordance with this priority commandthus providing a modified list. This indication may further specify atime constraint for the discontinuing step or even a time constraint formodifying or changing the channel list. Once the selective messagingunit receives the indication to discontinue monitoring the firstchannel, the receiver (317) as directed by or in cooperation with thecontroller (319) scans the channels of the modified list to provide asecond channel or operating channel. As the selective messaging unittraverses a hypothetical path of travel as previously discussed withreference to FIG. 1, the receiver (317) and the controller (319),responsive to an appropriate indication and the particularcircumstances, work together to scan for and select a channel, secondchannel, or operating channel for previous, intermediate, and divertedlocations. Under some circumstances such as equal priority channelswhere a unit is otherwise unable to resolve a proper operating channel,it can be advantageous for the indication to be an affirmation of thepresent operating channel thus avoiding unnecessary scanning.

Referring to FIG. 6, a process or method of selecting an operatingchannel for a selective messaging unit is depicted. The method begins orstarts at (603) after which step (605) provides a list of potentialoperating channels that is preferably a list received at, for example,activation. Next at step (607) monitoring a first channel, from thislist, for a message intended for or addressed to this selectivemessaging unit occurs. Step (611) detects or tests for, as part of themessage from step (607) an indication or priority indication. If no suchindication is found the process continues to monitor the first orinitial operating channel to check for this indication. If an indicationis found at step (611), step (613) tests to see whether the indicationis an affirmation of the present channel and if so step (607) isrepeated and if not the process continues at step (615). Step (615)looks or tests whether a priority command or channel priority indicationcorresponding to the list of potential operating channels in the scanlist and is included in the found or detected indication from step(611). If the indication is a priority command, step (617) operates tomodify the list of channels and their corresponding priorities inaccordance with the indication from step (611). If the step (615) testis negative or after step (617) is performed, step (619) is performedand the indication is tested to determine whether any time constraint isincluded. If this test is positive, step (621) checks whether the timeconstraint is satisfied. If not, the process returns to step (607) andcontinues to monitor the present channel. If the time constraint issatisfied at step (621) or none was included at step (619), step (623)operates to discontinue monitoring the present channel and step (625)initiates a scan of the channel list, as modified so, to find or selecta channel or the operating channel. After step (625) the monitoring step(607) is repeated. The channel list and contents is exemplified by thelist discussed above with reference to FIG. 4. The indication isexemplified by the FIG. 5 depiction of associated discussion. Referringto FIG. 7, a process or method (701) of scheduling messages on anoperating channel for a selective messaging unit is depicted. The methodbegins or starts at (703) after which, at step (705), the selectivemessaging system is provided a list of operating channels that can beused to schedule messages (705). Then, step (707) with reference to amessaging unit plan and various service parameters selects a pluralityof channels corresponding to the selective messaging unit. Step (711)then selects a second channel from this plurality of channels when thesecond channel preferably, corresponds to a destination area or systemfor the selective messaging unit. Step (713) then formulates anindication or channel priority indication that includes, when needed, arelative priority of the channels, as well as, any time constraints,such as when the present channel is no longer valid, etc. Step (715)schedules a message with the channel priority indication on the presentchannel after which step (717) determines whether time constraints aresatisfied. Note: once the scheduled delivery time of the message by theselective messaging system is reached, the message is transmitted withthe appropriate channel priority indication destined for the selectivemessaging unit. If not step (719) introduces a time delay where asubsequent message must be delivered and then a subsequent message needsto be delivered if it is scheduled on all or a subset of the pluralityof channels. If the time constraints are satisfied at step (717) orafter step (723), subsequent messages for the selective messaging unitare scheduled on the second channel at step (721) and the process endsat step (725). It will be advantageous if the plurality of channelsincludes previous location or intermediate location.

It will be appreciated by those of ordinary skill in the art that theapparatus and methods disclosed provide various inventive techniques foreffecting channel acquisition and thus facilitating roaming service fora messaging unit. The channel acquisition apparatus and methodsdiscussed have improved the ability to automatically allow selectivemessaging systems and selective messaging units to modify and effectoperating channel acquisition over known techniques. This has been donewithout compromising the accuracy of messaging and without otherwiseburdening processing resources in either the system controller or theselective messaging unit. These inventive structures and methods may bereadily and advantageously employed in a selective messaging system,selective messaging unit, or other communications devices or system.

The inventive principles disclosed herein allow roaming capability orservice and lower battery consumption in selective messaging units thanthose performing background scanning. Further a reduction in the numberduplicate transmissions among selective messaging systems is providedthus avoiding an unnecessary drain on system capacity. Hence, thepresent invention, in furtherance of satisfying a long-felt need ofmessaging systems, readily facilitates, roaming service and loadmanagement as well as low power consumption selective messaging units byproviding methods and apparatus for automatically and readily effectingchannel acquisition that are practical to implement from a physical,economic and power source perspective.

It will be apparent to those skilled in the art that the disclosedinvention may be modified in numerous ways and may assume manyembodiments other than the preferred forms specifically set out anddescribed above. Accordingly, it is intended by the appended claims tocover all modifications of the invention which fall within the truespirit and scope of the invention.

What is claimed is:
 1. In a selective messaging unit a method ofselecting an operating channel, said method including the stepsof:providing a list of potential operating channels, said list includinga first channel and a second channel; monitoring said first channel fora message addressed to the selective messaging unit; detecting as partof said message an indication further including a priority command andmodifying said list in accordance with said priority command to providea modified list during said step of monitoring; discontinuing,responsive to said indication, said step of monitoring; and thenscanning for said second channel to use as the operating channel.
 2. Themethod of claim 1 wherein said step of discontinuing is performed at atime corresponding to information within said indication.
 3. The methodof claim 1 wherein said step of scanning further includes scanningchannels corresponding to said modified list to provide said secondchannel.
 4. The method of claim 3 wherein said step of scanning channelsincludes scanning a channel for an intermediate location.
 5. The methodof claim 3 wherein said step of scanning channels includes scanning achannel for a diverted location.
 6. The method of claim 3 wherein saidstep of scanning channels includes scanning a channel for a previouslocation.
 7. In a selective messaging system a method of schedulingmessages on an operating channel for a selective messaging unit, themethod including the steps of:first scheduling a first message addressedto the selective messaging unit on a first channel, said first messageincluding a channel priority indication corresponding to said firstchannel; and second scheduling a second message for said selectivemessaging unit on a second channel, said second channel selected as theoperating channel from a plurality of channels as an alternative to saidfirst channel.
 8. The method of claim 7 wherein said step of secondscheduling said second message includes scheduling said second messageon each channel of said plurality of channels.
 9. The method of claim 7wherein said step of second scheduling is performed at a time determinedto correspond to said channel priority indication.
 10. The method ofclaim 7 wherein said step of second scheduling includes scheduling saidsecond message on a channel for an intermediate location.
 11. The methodof claim 7 wherein said step of second scheduling includes schedulingsaid second message on a channel for a previous location.
 12. The methodof claim 7 wherein said step of second scheduling includes schedulingsaid second message on a channel for a diverted location.
 13. The methodof claim 7 further including a step of providing a list of potentialoperating channels for the selective messaging unit, said list includingsaid plurality of channels.
 14. The method of claim 13 wherein said stepof first scheduling further includes formulating said channel priorityindication to correspond to a relative priority of channels within saidplurality of channels.
 15. A selective messaging unit arranged andconstructed for selecting an operating channel and comprising incombination:a memory for storing a list of potential operating channels,said list including a first channel and a second channel a receiver formonitoring said first channel for a message addressed to the selectivemessaging unit; and a controller, coupled to said receiver, fordetecting as part of said message an indication further including apriority command and modifying said list in accordance with saidpriority command to provide a modified list and responsive theretocausing said receiver to discontinue monitoring said first channel andthen scan for said second channel to use as the operating channel. 16.The selective messaging unit of claim 15 wherein said receiverdiscontinues monitoring said first channel at a time corresponding toinformation within said indication.
 17. The selective messaging unit ofclaim 15 wherein said controller cooperatively with said receiver scanschannels corresponding to said modified list to provide said secondchannel.
 18. The selective messaging unit of claim 17 wherein saidcontroller together with said receiver scans a channel for a divertedlocation.
 19. The selective messaging unit of claim 17 wherein saidcontroller together with said receiver scans a channel for a previouslocation.
 20. The selective messaging unit of claim 17 wherein saidcontroller together with said receiver scans a channel for anintermediate location.
 21. A messaging system controller for schedulingmessages on an operating channel for a selective messaging unit, themessaging system controller comprising in combination:a processor forscheduling a first message addressed to the selective messaging unit ona first channel, said first message including a channel priorityindication corresponding to said first channel; said processor thenscheduling a second message for said selective messaging unit on asecond channel, said second channel selected as the operating channelfrom a plurality of channels as an alternative to said first channel;and a transmitter port for coupling said first message and said secondmessage to corresponding transmitters.
 22. The messaging systemcontroller of claim 21 wherein said processor schedules said secondmessage on each channel of said plurality of channels.
 23. The messagingsystem controller of claim 21 wherein said processor schedules saidsecond message on a channel for a diverted location.
 24. The messagingsystem controller of claim 21 wherein said processor schedules saidsecond message on a channel for a previous location.
 25. The messagingsystem controller of claim 21 wherein said processor schedules saidsecond message on a channel for an intermediate location.
 26. Themessaging system controller of claim 21 wherein said processor schedulessaid second message at a time determined to correspond to said channelpriority indication.
 27. The messaging system controller of claim 21further including a memory for storing a list of potential operatingchannels for the selective messaging unit, said list including saidplurality of channels.
 28. The messaging system controller of claim 27wherein said step of first scheduling further includes formulating saidchannel priority indication to correspond to a relative priority ofchannels within said plurality of channels.